In autumn weather, mud fever can be a problem for horses and owners. But we explain why it’s not just a rainy-day problem, and how you can prevent it.

What is mud fever, and why does it happen?

Mud fever is one of the most common skin conditions seen in horses and ponies. It is more correctly described as “bacterial dermatitis”, meaning inflammation of the skin caused by a bacterial infection. Generally, the condition is limited to the skin on the lower limbs, especially the back of the heels and pastern areas- but it can sometimes also involve the cannon regions. White-haired areas with pink skin underneath are often worst affected. Similar bacterial infections can also cause problems on other parts of the body; however, if the skin on the back, neck, or hindquarters are affected, this is usually referred to as rain scald.

A reduction of the skin's natural defences or skin damage can allow commensal bacteria (i.e. bacteria that live on the skin all the time) to take hold and cause an infection. These include Dermatophytosis congolensis, Staphylococcus species, and Streptococcus species. These bacteria may be the primary problem, or they may be causing a secondary bacterial infection alongside another underlying skin issue.

Mud fever can be seen at different times of the year, depending on the weather conditions. It typically occurs due to continuous or repeated wetting of the skin, which is a common problem in the UK during the autumn and winter months. However, it can also occur when the ground is dry. The following situations increase the chances of mud fever developing:

  • heavy dew on the grass each morning
  • daily washing/hosing of the legs without drying the skin
  • high temperature
  • high humidity
  • arena or turnout pen surfaces (especially sand, or surfaces containing silica, as these are very abrasive)
  • irritation from boots or overreach boots (especially if dirty or greasy)
  • contact reactions to certain types of plant
  • sunburn

How is mud fever diagnosed, and why should we be worried about it?

Mud fever in horses is usually diagnosed on the appearance of a horse or pony’s skin, i.e. scabs on the lower limbs, serous discharge, crusting, redness, tufty hair or open sores. These skin lesions are often seen together with swelling of the leg. Although many mild cases will respond to basic treatment, in more severe cases complications can include cellulitis (infection or inflammation of deeper tissues), lymphangitis (inflammation of the lymphatic drainage system leading to extensive swelling), and lameness. The skin may take a long time to heal, and if the affected areas are extensive or particularly deep, this healing process can take several months and may result in scarring of the skin.

There are many other causes of dermatitis which may look like mud fever in horses, or may contribute to mud fever signs, so it may be necessary to consult your vet if in doubt about what is causing your horse or pony’s skin condition. Such other conditions include chorioptic mange (mite infestation), sunburn, dermatophytosis (ringworm), photosensitisation, liver disease, coronary band dystrophy, and leucocytoclastic vasculitis (a hypersensitivity reaction).

With that in mind, there are diagnostic tests available which may be recommended for horses or ponies which repeatedly suffer from mud fever, or for those cases which do not respond well to initial treatment. These tests may include:

  • blood tests – to look for an underlying medical problem e.g. liver disease
  • swabbing discharge, or swabbing/sampling the scabs – this can check what type of bacteria are present if your vet is considering prescribing antibiotics, or if there is a suspicion that they are resistant to any antibiotics already being used
  • skin biopsies – this can help to distinguish between different types and causes of skin inflammation, and help work out the most appropriate treatment
  • skin scrapes – this is useful for detecting mites in case these are contributing to the irritation

How is mud fever treated?

Treatment of mud fever varies between cases depending on the severity; however, it is likely to involve the following key things:

Clipping hair

Clipping hair away from the affected area helps you to see the extent of the problem and allows better access for cleaning, scab removal, drying and applying creams. Where horses are very sore, they may require sedation for clipping.

Removing scabs

This is really important because the bacteria that cause mud fever live underneath the scabs. Removing the scabs exposes them, meaning topical treatment is more effective. Some horses may require softening of scabs with a poultice/cling film before they can be removed. Once this has been done, scabs should be removed frequently to avoid them building up

Washing and skin care

The skin should then be washed using an anti-bacterial solution. For many products, contact time is crucial. Typically, leaving the shampoo on the skin for ten minutes and then rinsing with plain warm water is recommended, but your shampoo will give you instructions. Drying the skin after washing is very important and should be done with disposable material such as paper towel to avoid harbouring or spreading bacteria. You should then apply an anti-bacterial cream to the affected area(s) of skin. Most anti-bacterial creams for mud fever are very gentle on the skin. Stabling may be necessary to allow skin healing, especially where weather is poor- if this is the case bedding must be kept as clean and dry as possible.

If cases are not responding to basic treatment, the horse’s skin is very painful, or the areas are very extensive, veterinary examination may be required to see whether further investigation or treatment is indicated. These further treatments may include:

  • treatment of any underlying cause e.g. mites or liver disease
  • steroid cream
  • non-steroidal anti-inflammatories
  • antibiotics or topical antibiotic spray
  • steroids

What can be done to prevent mud fever in horses?

Preventing mud fever in horses isn’t easy, but there are a few things you can do to reduce the chance of mud fever occurring. Hosing a horse or pony’s legs off when bringing them in from the field can drive mud, dirt, and bacteria further towards the skin, and they may even take longer to dry. Even though the legs may look cleaner with hosing, it is often better to let the legs dry and then brush the mud off later. Care must be taken if using bandages to help them to dry as these may shrink and cause further problems.

Waterproof mud fever barrier creams can be useful as a preventative measure but are not recommended as a treatment if mud fever lesions have already developed- this is because they will trap the bacteria against the skin and slow the healing process. Sun cream should always be considered in the summer, especially for white-haired areas with pink skin underneath. If turnout boots are being used these must be clean and dry every time they are worn, otherwise they may exacerbate the problem by causing local skin damage or irritation.

Unfortunately, mud fever is likely to recur in many horses, but the above steps can reduce the frequency of episodes. Regular skin checks- and prompt treatment when needed- can also help you to get on top of any problems quickly.

Article written by Jessica Putnam